1. Field of the Invention
The present invention relates to a discriminating device for discriminating between two kinds of objects of determination based on the reflected light thereof.
2. Description of the Related Art
A technique has been developed, wherein a printing plate (hereinafter referred to as a photopolymer plate) having a photosensitive layer (for example, a photopolymerization layer) provided on a support is used and an image is directly recorded on the photopolymerization layer of the photopolymer plate by a laser beam or the like (an automatic exposure apparatus for printing plates).
In such a technique, a plurality of photopolymer plates accommodated in a magazine are taken out one-by-one from the magazine and transferred to an exposure section in which the above-described recording of images is carried out. Further, immediately before the exposure section, the photopolymer plate is basically placed on a smooth surface table and registered on the surface table, and thereafter, the photopolymer plate is transferred to the exposure section together with the surface table.
The photopolymer plates are stacked in the above-described magazine, and interleaf papers are interposed between the photopolymer plates so that the photopolymer plates and the interleaf papers are alternately stacked with one another. If a photopolymer plate is located at the uppermost position of the stack, the photopolymer plate is transferred to the exposure section as described above. If an interleaf paper is disposed at the uppermost position of the stack, the interleaf paper needs to be discharged from a conveying path to the exposure section without being transferred to the exposure section.
Accordingly, a discriminating device structured to include a laser light source disposed above the stack of photopolymer plates and interleaf papers, and a laser reflection sensor which receives laser light reflected by a surface of photopolymer plate or interleaf paper, is used to discriminate between photopolymer plate and interleaf paper based on the intensity of reflected laser light.
However, the laser reflection sensor which receives laser light is adapted to generate a signal corresponding to the intensity of received laser light, and therefore, the structure thereof is complicated and expensive. As a result, when such a laser reflection sensor is used, the discriminating device, and further, an automatic exposure apparatus for printing plates may increase in costs.
In view of the above-described facts, an object of the present invention is to provide a discriminating device by which two kinds of objects of determination having different surface reflectivities can be discriminated at a low cost.
A first aspect of the present invention is a discriminating device for discriminating between two kinds of objects of determination, which have different surface reflectivities, comprising: a first optical sensor having a light receiving portion which receives light reflected by surfaces of the objects of determination, the first optical sensor reacting to either reflected light from the two kinds of objects of determination; and a second optical sensor having a light receiving portion which receives the reflected light, the second optical sensor being provided so as to react to reflected light from one of the objects of determination, of which surface reflectivity is higher, and so as not to react to reflected light from the other object of determination of which surface reflectivity is lower.
In the discriminating device having the above-described structure, both the first optical sensor and the second optical sensor receive the reflected light from the objects of determination. First, the first optical sensor is brought into a state of reacting to either reflected light from the two kinds of objects of determination. As a result, at least a state in which the two kinds of objects of determination are located at a predetermined position to be determined, is detected, and a discrimination between the two kinds of objects can be started. Next, if the second optical sensor is in a reactive state, it can be determined that an object to be determined is one of the two kinds of objects having a higher surface reflectivity. If the second optical sensor is in a nonreactive state, it can be determined that an object to be determined is the other one of the two kinds of objects having a lower surface reflectivity. Further, for example, if the first optical sensor is in a nonreactive state, it can be determined that none of the two kinds of objects is located at a position at which the reflected light can be received by the first and second optical sensors (there are cases in which others than the two kinds of objects may be located).
As described above, the discriminating device of the present invention is adapted to discriminate between the two kinds of objects based on the difference of light-receiving level between the two kinds of optical sensors. Therefore, low-cost and general purpose optical sensors suffice. As a result, the cost of apparatus itself can be reduced.
In the discriminating device according to the first aspect of the present invention, preferably, the light receiving portion of the first optical sensor is made to face an optical axis of the reflected light, and the light receiving portion of the second optical sensor is inclined to the optical axis of the reflected light.
In the discriminating device having the above-described structure, the light receiving portion of the first optical sensor is disposed so as to face the optical axis of the reflected light, but the light receiving portion of the second optical sensor is inclined to the optical axis of the reflected light. Therefore, even if the first optical sensor and the second optical sensor have the same light-receiving level, the reflected light is obliquely received by the second optical sensor, and the light-receiving level of the second optical sensor substantially becomes low. For this reason, optical sensors of the same standard can be used for the first optical sensor and the second optical sensor, thereby resulting in that the cost of the device can be further reduced.
In the above-described discriminating device, more preferably, the first optical sensor and the second optical sensor do not each react to reflected light from a portion in which the two kinds of objects of determination are placed.
In the above-described discriminating device, neither the first optical sensor nor the second optical sensor reacts to light reflected by a portion in which the objects of determination are placed. Therefore, a state in which neither of the two kinds of objects of determination is placed in the above-described portion, can be detected.
In any one of the above-described discriminating devices, still more preferably, a printing plate on which an image is recorded, is used as one of the two kinds of objects of determination, and an interleaf paper of which surface reflectivity is different from that of the printing plate and which is interposed between stacked printing plates, is used as the other one of the two kinds of objects of determination.
In the discriminating device having the above-described structure, one of the two kinds of objects of determination is a printing plate and the other is an interleaf paper interposed between a plurality of printing plates. In this aspect, normally, respective subsequent processing for the printing paper and interleaf paper is different from each other. When it is determined by the discriminating device whether an object to be determined is the printing paper or the interleaf paper based on the difference of surface reflectivity between the printing plate and the interleaf paper, the printing plate and the interleaf paper can be processed in a process corresponding to each of the printing plate and the interleaf paper.